1. Field of the Invention
The present invention relates to an illumination system, and more particularly, to an illumination system for a projection apparatus.
2. Descriptions of the Related Art
Due to advantages such as a short startup time and a long service life, light emitting diodes (LEDs) have been widely used as light sources of common projection apparatuses in place of conventional high-pressure mercury lamps (HPLs).
Generally, a projection system uses LEDs to provide light beams of the three primary colors (i.e., red, green and blue) that are projected in different directions, and then, the light beams of the three primary colors are combined by a light combining element into a full-color (i.e., white color) light beam for projection to a light valve (e.g., a DMD, an LCD or an LCoS) of a projection apparatus. However, as compared to the intensities of the red light beam provided by the red LED or the blue light beam provided by the blue LED, the intensity of the green light beam provided by the green LED is weaker. As a consequence, the brightness of the green color of the image projected by the projection apparatus is relatively low, which makes the image look unnatural.
Therefore, an illumination system capable of enhancing the intensity of the green light has been developed in the art. FIG. 1 illustrates an illumination system 1 that comprises a red LED 11, two blue LEDs 13, 15, and an ultraviolet (UV) LED 17. The red LED 11 and the blue LED 13 are adapted to provide a red light beam and a blue light beam respectively for the illumination system 1. The blue LED 15 and the UV LED 17 are adapted to excite a green phosphor 12 via two light splitters 19a, 19b respectively to provide a green light beam of an adequate intensity for the illumination system 1.
Because the illumination system 1 needs to use more than one light splitters and each of the LEDs must be provided with a lens, the size of the projection apparatus is increased. If the volume of the projection apparatus needs to be reduced, the structure of the illumination system must be reduced, which would cause a decrease in the brightness thereof. Furthermore, the green light beam provided by the illumination system 1 does not have an adequate intensity that matches the intensities of the red light beam and the blue light beam.
Accordingly, it is important to provide an illumination system that can enhance the intensity of a light beam of a specific color (e.g., the green light) and that has a reduced volume.